When the great land masses of Africa and India collide with Europe and Asia, about 100 million years ago, they cause the crust of the earth to crumple upwards in a long almost continuous ridge of high ground - from the Alps, through Turkey, Iran and Afghanistan to the Himalayas. This barrier will have a profound influence on human history.

To the south and east of the mountain range are various fertile regions, watered by great rivers flowing from the mountains. By contrast, north of the mountain range is a continuous strip of less fertile grasslands - the steppes, on which a horseman can ride almost without interruption from Mongolia to Moscow.

This unbroken stretch of land north of the mountains, reaching from the Pacific in the east to the Atlantic in the west, means that the boundary between Asia and Europe is a somewhat vague concept. Indeed Europe is really the western peninsula of the much larger mass of Asia.

In the south there is a natural barrier, long accepted as a dividing line - formed by the waters of the Dardanelles, the Sea of Marmara, the Bosphorus and the Black Sea. North from here the boundary is notional. In recent times it has been accepted as passing east from the Black Sea to the Caspian and then stretching north from the Caspian along the eastern slopes of the Ural mountains.

The first Europeans: 500,000 - 10,000 years ago

Early man - of the species Homo erectus - penetrates to the western extremity of Europe by about 500,000 years ago. Fossil remains from this time are known as far west as England.

From about 230,000 years ago the human inhabitants of Europe, descendants of Homo erectus, are sufficiently different in brain size and physique to be classed as an early form of Homo sapiens. Known as Neanderthal man, this species prospers for many thousands of years. But the Neanderthalers leave little trace of themselves other than their stone tools, their bones and the bones of their animal prey (though a recently discovered Neanderthal flute suggests some cultural life). They are extinct by about 35,000 years ago.

Modern man - anatomically similar to humans today - arrives relatively late in Europe. But the continent does provide the most extensive evidence of the early culture of our own species of Homo sapiens.

The Venus of Willendorf (about 25,000 years ago) and the cave paintings of Altamira and Lascaux (some 15,000 years ago) are merely the most famous examples of a vigorous palaeolithic art found in many parts of Europe. Similarly the exposed plains of eastern Europe contain traces of the earliest known free-standing dwellings - circular huts, semi-sunken, with stones or tusks supporting some form of superstructure.

From villages to towns in Europe: 7000 - 2000 BC

The Neolithic Revolution - introducing village life, the cultivation of crops and the rearing of animals - arrives in Greece in about 7000 BC from its region of origin in the Middle East. It will take about 3000 years to spread to the Atlantic coast and Britain, pushing back the way of life of the hunter-gatherers at an average rate of slightly more than a mile a year.

This slow rate of progress may partly reflect a reluctance of the hunter-gatherers to settle down to the hard labour of agriculture. But it is due also to the fact that here the labour is indeed hard. Europe, unlike the Middle East, is heavily forested. Clearing the ground for crops, with stone tools, is a massive undertaking.

In the Atlantic coastal regions, the transition to neolithic village settlement is marked by the world's most striking tradition of prehistoric architecture.

In most of Europe neolithic communities live in villages of timber houses, often with a communal longhouse as the central feature (one, discovered at Bochum in Germany, is some 65 metres in length). But along the entire Atlantic coast, from Spain to Britain and Denmark, the focus of village life is a communal tomb, around which simple huts are clustered. The tomb chambers of these regions introduce the tradition of stonework which includes passage graves and megaliths, also the very solid domestic architecture of Skara Brae.

By the time the whole of Europe has entered the neolithic age, the eastern Mediterranean - where Africa joins Asia - is literate and civilized. Like farming, civilization spreads by contagion from Asia to Europe. The point where the two continents meet, round the Aegean Sea, becomes from around 2000 BC the site of Europe's first civilization - that of Minoan Crete.

Minoan civilization, after several centuries, yields to an incoming group which eventually provides nearly all the peoples of Europe - the Indo-Europeans.

Indo-Europeans: from 2000 BC

Tribes speaking Indo-European languages, and living as nomadic herdsmen, are well established by about 2000 BC in the steppes which stretch from the Ukraine eastwards, to the regions north of the Black Sea and the Caspian.

Over the coming centuries they steadily infiltrate the more appealing regions to the south and west - occasionally in something akin to open warfare, and invariably no doubt with violence. But the process is much more gradual than our modern notions of an invading force.

Indo-Europeans in Europe: from 1800 BC

In Europe the first Indo-European tribes to make significant inroads are the Greeks. They move south into Greece and the Aegean from the 18th century BC.

Gradually other tribes speaking Indo-European languages spread throughout Europe. From an early date Germans are established in Denmark and southern Sweden. Balts settle along the southern and eastern coast of the Baltic Sea. Tribes using an Italic group of languages descend into Italy. Across the centre of Europe the Celts move gradually west through Germany into France, northern Spain and Britain.

Another wave of migrating Indo-European peoples follows on behind, pressing westwards from Asia. The Slavs move into the region of Poland and western Russia, between the Vistula and Dnieper rivers. The Scythians establish themselves in the area to the north of the Black Sea.

Any map will oversimplify patterns of tribal migration, for it must attempt to separate groups which in reality intermingle and overlap. If there is not too much pressure on the available territory, different tribes often coexist within a region. Even so, in broad terms, the tribes mentioned here from the great majority of Europeans at the time when Greece and Rome dominate the Mediterranean region.